In May 2004, a volume of 600,000 acre-feet is scheduled to be released from Lake Powell, which is an average of 9,760 cubic feet per second(cfs). On Mondays through Fridays in May, daily fluctuations due to load following will likely vary between a low of about 6,600 cfs during late evening and early morning off-peak hours) to a high of about 12,600 cfs (during late afternoon and early evening on-peak hours). On Saturdays, releases will likely vary between a low of about 6,600 cfs during off-peak hours to a high of about 11,800 cfs during on-peak hours. On Sundays, releases will likely vary between a low of about 6,600 cfs during off-peak hours to a high of about 11,000 cfs during on-peak hours. A volume of 800,000 acre-feet is scheduled to be released in June which is an average release of 13,400 cfs.
Because of the draw down condition of Lake Powell, releases from Lake Powell in water year 2004 are being scheduled to meet the minimum release objective of 8.23 million acre-feet. This is consistent with the requirements of the Criteria for Coordinated Long-Range Operation of Colorado River Reservoirs.
Upper Colorado River Basin Hydrology
The month of March pretty much dashed hopes that 2004 would bring relief to the ongoing drought in the Colorado River Basin. Basin snowpack on March 1, 2004 was 96 percent of average. At that time the April through July inflow was forecasted to be 82 percent of average. The weather pattern in March, 2004 was very dry and extremely warm for early spring. Temperatures around the basin for much of the month were 20 degrees above average. Basinwide snowpack dropped over 30 percentage points in March.
In April, aggregate precipitation in the Upper Colorado River Basin was near average, with the southern portion of the basin receiving above average precipitation, and the northern regions below. As of May 3, 2004 basinwide snowpack is 61 percent of average. The National Weather Service April mid-month forecast is calling for 4.0 million acre-feet of unregulated inflow to Lake Powell during the April through July runoff period, only 50 percent of average. This is a sizable reduction from the volume forecasted in March. A revised forecast will be issued the week of May 3.
The drought continues. The Colorado River Basin is now in its 5th year of drought. Inflow volumes have been below average for 4 consecutive years, with 2004 almost certain to follow suit. Unregulated inflow in water year 2003 was only 53 percent of average. Unregulated inflow in 2000, 2001 and 2002 was 62, 59, and 25 percent of average, respectively.
Inflow in 2002 was the lowest ever observed since the completion of Glen Canyon Dam in 1963.
Inflow to Lake Powell in March and April approached average levels as abnormally warm temperatures melted out significant amounts of snow in the basin. Unregulated inflow in March was 538,000 acre-feet, 81 percent of average. April unregulated inflow was 816,000 acre-feet, 83 percent of average. Unfortunately the inflows seen in March and April will be at the expense of May and June inflows (when the largest inflow volumes are normally observed). As of May 2, 2004 inflow to Lake Powell is 9,000 cfs about 45 percent of what is normally seen in early May. Low inflows the past 5 years have reduced water storage in Lake Powell. The current elevation (as of May 2, 2004) of Lake Powell is 3,587 feet (113 feet from full pool). Current storage is 10.2 million acre-feet (42 percent of live capacity).
The water surface elevation of Lake Powell has reached its seasonal low. The water surface elevation will increase incrementally in May and June, likely reaching a high of about 3,590 feet in mid-June. By late June the water surface elevation will likely begin to decrease. It's almost certain that Lake Powell will remain below elevation 3,600 feet in 2004. Under the current inflow forecast, the water surface elevation of Lake Powell is projected to be 3,574 feet on January 1, 2005. It should be noted that this projected elevation will likely shift, depending upon weather patterns the remainder of the year.
Courtesy Tom Ryan, US Bureau of Reclamation